Titanium is a light weight, noncorrosive, high strength-to-weight metal that is extensively used in the aircraft industry, and, more recently, in the chemical process industry and energy related fields.
Currently, titanium is made by the Kroll Process, which is disclosed in U.S. Pat. No. 2,205,854. While the Kroll process uses magnesium in the reduction step, it is also known to use sodium reduction, as set forth by Hunter in Metallic Titanium, (J. Am. Chem. Soc., v. 32, 1910 p. 330.).
Kroll and Hunter use rutile, a rutile substitute or upgraded ilmenite as the raw material. In these processes, the raw materials are chlorinated to produce titanium tetrachloride and other impurity chlorides, followed by distillation, wherein the titanium tetrachloride is separated from the other chlorides, and then reduced by magnesium or sodium, to produce titanium sponge. This sponge is purified by vacuum distillation, helium sweep or leaching, and then pressed into electrodes which are arc melted up to three times to consolidate and purify the titanium while blending in alloying elements. In general, the disadvantages of the Kroll and Hunter processes include non-continuous operation, numerous processing steps, and high energy consumption.
Some early attempts to provide processes for producing titanium that are continuous, less costly, and utilize fewer and simpler steps involved the use of fluoride salts as titanium extraction agents for oxide ores, such as ilmenite. These are disclosed in U.S. Pat. Nos. 2,418,073; 2,418,074; 2,653,855; 2,813,068; 2,823,991 and 2,837,426.
Despite the innovative use of fluoride salts in the aforementioned patents, there was still the need in the industry to provide a simpler, more direct route to titanium metal, which used chemical reduction of the fluotitanate salts directly to titanium metal.
U.S. Pat. No. 4,390,365 which is incorporated wherein by reference attempts to achieve this, and discloses a process for converting a titanium oxide ore, such as ilmenite into titanium by fluorinating titanium oxide, reducing the formed titanium fluoride to titanium metal by contacting the titanium fluoride with a molten alloy of zinc and aluminum, recovering the titanium-zinc alloy from the aluminum fluoride residue, removing the zinc from the alloy by distillation, and leaving titanium metal. However, in the removal of zinc, there is risk of residual zinc contamination. Moreover, the process is noncontinuous and the production of substantial amounts of environmentally hazardous aluminum fluoride compounds are readily apparent disadvantages of this process.
Titanium and its alloys are reactive metals as temperatures above about 650.degree. C., have high melting points, and, when molten, react with most materials commonly used for their containment.
Thus, the preferred reactor for the reduction of fluotitanate salts should provide: (1) a reactor enclosure that is nonreactive with the titanium and byproducts, (2) a reaction volume with sufficient residence time to complete the reaction, (3) input of heat to maintain the reactants, titanium and other reaction products in the molten state, (4) mixing reactants and products to insure reactant availability for reaction and product homogeneity, and (5) a method to remove products and byproducts to make the process continuous.
U.S. Pat. No. 3,775,091 provides such an ideal reactor in an apparatus designed to melt refractory metals such as titanium, zirconium and their alloys in an induction heated, liquid cooled segmented copper crucible. The bottom of the crucible is formed by the cooled melt material and a continuous metal ingot of the desired material may produced and withdrawn. Calcium fluoride and the refractory metal are fed into the crucible where the calcium fluoride forms an insulating layer to protect the cooled copper. Water cooled copper coils around the crucible carry the alternating current for the induction heating.